1. Field of the Inventions
The present invention relates to an image pickup apparatus and, more particularly, to exposure control and white balance control for the image pickup apparatus.
2. Description of the Related Art
The advance of image pickup apparatuses, such as video cameras, has heretofore been remarkable, and the number of functions per apparatus has been becoming larger and larger.
One example of a conventional image pickup apparatus is shown in FIG. 1 in block form.
The image pickup apparatus shown in FIG. 1 includes a zoom lens 1 which is made from a lens group for forming an image of a subject and has a focal length which can be varied, an iris mechanism 3 such as an iris having an iris blade structure for controlling the amount of incident light or a liquid crystal plate for controlling the amount of passing light (in this example, the iris mechanism 3 employs an iris), a driving motor 4 for driving the iris mechanism 3, iris mechanism driving means 5 for driving the driving motor 4, an image pickup element 6 for photoelectrically converting incident light, image pickup element driving means 7 for controlling the image pickup element 6 to read a photoelectric signal therefrom and for controlling a signal storage time, i.e, a so-called electric shutter function, CDS(correlation double sampling)/AGC means 8 for performing automatic gain control (hereinafter referred to as xe2x80x9cAGCxe2x80x9d) for sampling the photoelectric signal supplied from the image pickup element 6 and electrically amplifying the sampled signal, analog-digital conversion means 9 for converting the analog signal outputted from the CDS/AGC means 8 into a digital signal, camera signal processing means 10 for applying processing, such as gamma correction, color separation and color-difference matrix transformation, to the digital signal and adding a synchronizing signal to the processed digital signal to produce a standard television signal, digital-analog conversion means 11 for converting the output signal of the camera signal processing means 10 from digital state to analog state, electronic image magnifying processing means 12 for taking out a signal from the front stage of the camera signal processing means 10, electrically performing image magnifying processing of the signal and returning the processed signal to the camera signal processing means 10, and a microcomputer 15 which has exposure control means for controlling exposure by controlling the iris mechanism 3, the electronic shutter function of the image pickup element 6 and the AGC of the CDS/AGC means 8, and control means for controlling the electronic image magnifying processing means 12.
The image pickup apparatus having the above-described arrangement includes means which enables a subject aimed at by a photographer to be photographed as an image magnified to a size desired by the photographer. As such means, there are an optical-zoom function for varying the focal length of the zoom lens 1 and optically controlling the size of a subject image to be formed on the image pickup element 6 and a so-called electronic-zoom function for electrically magnifying an image by using the electronic image magnifying processing means 12.
The image pickup apparatus also includes photographing-operation assistant means which assists in a photographing operation. As such photographing-operation assistant means, there are automatic exposure control means for automatically performing optimum control of the state of exposure of a subject, automatic white balance control means for automatically adjusting color temperature, i.e., automatically optimizing the state of white balance, and the like. These photographing-operation assistant means are intended to enable a photographer to obtain an optimum image through a simple photographing operation even if the photographer varies the size of a subject image by using the zoom lens 1 or the electronic image magnifying processing means 12, or even if the photographer carries out photography at any place under any situation.
The automatic exposure control means which is one of the photographing-operation assistant means will be described below.
The automatic exposure control means is controlled by the exposure control means of the microcomputer 15 according to the control flowchart shown in FIG. 2. First, in an exposure data detecting step S1001, the automatic exposure control means obtains exposure data by detecting a variation in the brightness of a subject from a luminance level contained in a video signal supplied from the camera signal processing means 10.
In the exposure data detecting step S1001, to obtain the exposure data, the automatic exposure control means detects a signal which has not yet been subjected to the processing of the electronic image magnifying processing means 12, or only a video signal corresponding to a magnified area if electronic image magnifying processing is performed. However, the automatic exposure control means may detect a signal which has been subjected to the processing of the electronic image magnifying processing means 12.
Then, the automatic exposure control means determines whether the state of exposure is correct, from the signal detected in the exposure data detecting step S1001, and if the state of exposure is correct (S1002, YES), the automatic exposure control means outputs the current exposure control value, Eo, without performing correction (S1009). If the state of exposure is not correct (S1002, NO), the process proceeds to an amount-of-exposure-correction computing step S1003, in which, on the basis of the detected signal obtained in the exposure data detecting step S1001, the automatic exposure control means selects exposure control parameters from among the iris mechanism 3, an electronic shutter which controls the storage time of the image pickup element 6, the gain of the AGC of the CDS/AGC means 9 and the like, and computes the amount of exposure correction, C, relative to each selected exposure control parameter (S1003). Then, if the state of exposure is brighter than a correct value (S1004, YES), the process proceeds to an exposure-control-value decreasing processing step S1006, in which the state of exposure is made darker. If the state of exposure is not brighter than the correct value (S1004, NO), the process proceeds to an exposure-control-value increasing processing step S1005, in which the state of exposure is made brighter. In either of the exposure-control-value decreasing processing step S1006 and the exposure-control-value increasing processing step S1005, an exposure control value En is obtained by correcting the exposure control value Eo which is currently outputted, by using the amount of exposure correction, C, computed in the amount-of-exposure-correction computing step S1003. Then, the exposure control value Eo is updated with the exposure control value En obtained by correcting the exposure control value Eo which is currently outputted (S1007), and the automatic exposure control means outputs the updated exposure control value Eo (S1009). Thus, the automatic exposure control means can effect the control of providing optimum exposure which can follow variations in the brightness of a subject at all times, so that the automatic exposure control means can automatically perform optimum exposure control without compelling the photographer to perform a bothersome manual operation, even if the brightness of the subject varies.
The automatic white balance control means is controlled according to the control flowchart shown in FIG. 3. First, the automatic white balance control means detects a variation in the color of a subject from a video signal supplied from the camera signal processing means 10 (S1101), and determines whether the state of white balance is correct, from the signal (color data) detected in Step S1101 (S1102). If the state of white balance is correct (S1102, YES), the automatic white balance control means outputs the current color gain control value, Co, without performing correction (S1105). If the state of white balance is not correct (S1102, NO), the automatic white balance control means computes a color gain correction value Cn (S1103). Then, the color gain correction value Co is updated with the color gain correction value Cn (S1104), and the automatic white balance control means outputs the updated color gain correction value Co (S1105). Thus, the automatic white balance control means can automatically effect optimum white balance control without compelling the photographer to perform a bothersome manual operation, even if the state of white balance varies. Incidentally, although the color data is obtained by detecting a signal which has been subjected to the processing of the electronic image magnifying processing means 12, the color data may be obtained by detecting a signal which has not yet been subjected to the processing of the electronic image magnifying processing means 12.
In recent years, more photographers have had more opportunities to perform photography of higher image magnifying rates owing to the development of zoom lenses having higher zoom magnifications or owing to the spread of use of the electronic image magnifying means. However, in the case of photography of high image magnifying rates, a field of view or a subject image tends to greatly vary with a small vibration of the image pickup apparatus due to a hand shake or the like, and the brightness or the state of color of a subject at which the image pickup apparatus is aimed greatly varies. In other words, the above-described automatic exposure control means at all times controls the state of exposure according to the brightness of light which is reflected from a subject and passes through the zoom lens 1, so that the automatic exposure control means sensitively follows even a small variation in the field of view or the subject image during the photography of high image magnifying rates and a variation occurs in the brightness of a main subject to be located within the image plane of the image pickup apparatus.
In addition, since the automatic white balance control means similarly sensitively follows a variation in the field of view or the subject image, a variation occurs not only in the state of exposure of the main subject but also in the state of white balance of the main subject, so that a visually greatly impaired image is formed.
It is, therefore, one object of the present invention to provide an image pickup apparatus which is capable of performing smooth exposure control and smooth white balance control even if image magnifying means is used to perform the processing of magnifying an image.
To achieve the above object, in accordance with one aspect of the present invention, there is provided an image pickup apparatus which comprises image pickup means, adjusting means for adjusting a state of a picked-up image by performing predetermined processing on a picked-up image signal outputted from the image pickup means, image magnifying means for magnifying an image, and control means for controlling a response characteristic of the adjusting means according to an image magnifying rate of the image magnifying means.
In accordance with another aspect of the present invention, there is provided an image pickup apparatus which comprises a photographing optical system, an image pickup element for picking up an image formed by the photographing optical system, image signal processing means for performing processing on an output signal of the image pickup element and producing a predetermined image signal, exposure control means for controlling a state of exposure of the image pickup element, image magnifying means for magnifying a size of an image represented by the predetermined image signal, and control means for controlling a response characteristic of the exposure control means in accordance with an image magnifying rate of the image magnifying means.
In accordance with another aspect of the present invention, there is provided an image pickup apparatus which comprises a photographing optical system, an image pickup element for picking up an image formed by the photographing optical system, image signal processing means for performing processing on an output signal of the image pickup element and producing a predetermined image signal, white balance control means for controlling a white balance of the predetermined image signal, image magnifying means for magnifying a size of an image represented by the predetermined image signal, and control means for controlling a response characteristic of the white balance control means in accordance with an image magnifying rate of the image magnifying means.
The above and other objects and aspects of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.